Observations on the structure and nature of flustrae [Part 2] / by R. E. Grant.

Date:
[1827]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the structure and nature of flustrae [Part 2] / by R. E. Grant. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    v rally a yellowish-grey colour, and a rough surface covered with minute reverted spines; they are variously subdivided, but most frequently present a broad palmate form, terminated by nume- rous rounded and expanded digitations. The sides of die stems and lower branches do not present the thickened, opaque, and compact margins we find in the F. trimeata and F. carbasea, which are much more delicate species. The tips of the branches are thin, soft, and transparent, as in other branched species, and as in the anterior margin of sessile species, from their containing little calcareous matter, and from the polypi in that situation be- ing young, colourless, and translucent. The boundaries of the cells on the opposite plains do not coincide, nor have they any determinate relation to each other in their position. The broad rounded extremity and the aperture of the cells are always above, the contracted and flat base always below. The cells are arranged on each surface, as in the F. carbasea; the opaque sides of the cells form continuous ramified lines from the base to the apex of the branches; and the first cell of a new series in the middle of the branch is always smaller than the cells which surround it, being confined to a small angular space, formed by the bifurcation of the opaque lateral wall of a per- fect cell. The tips of the branches are never bounded by a smooth continuous line, as we observe them in the F. carbasea and F. truncata, but are terminated by the round bulbous ex- tremities of the last two rows of cells; this remarkable difference is observable by the aid of a common lens. The cells are shorter and proportionally broader than in the F. carbasea, being about the sixth of a line in length, and a little more than half as much in breadth. By tearing the two plains of cells asunder, we render them nearly as transparent as in the F. carbasea, and can distinctly perceive the structure of the parts within. The aperture of the cells is formed by a semicir- cular lid, convex externally and concave internally, which folds down when the polypus is about to advance from the cell. The opening of this lid in the F. truncata, where it is very long, ap- pears through the microscope like the opening of a snake’s jaws, and the organs by which this motion is effected are not percep- tible. The lid of the cells opens and shuts in Jlustrce, without the slightest perceptible synchronous motion of the polypi. We